High pressure generating anvils



Oct. 10, 1967 R. D. POTTER 3,345,717

HIGH PRESSURE GENERATING ANVILS Filed March 11, 1965 RICHARD D. POTTE R INVENTOR.

M Wan/M ATTORNEY 3,345,717 HIGH PRESSURE GENERATING ANVILS Richard D. Potter, Fort Worth, Tex., assignor to General Dynamics Corporation, Fort Worth, Tex., a corporation of Delaware Filed Mar. 11, 1965, Ser. No. 439,036 1 Claim. (Cl. 25-402) ABSTRACT OF THE DISCLOSURE An ultra-high pressure anvil comprising a high-speed tool steel incorporating therein carbide grains bonded within the steel matrix so that, when hardened, the matrix itself is comprised of a hard, highly alloyed martensite having complex carbides therein, to which has been added additional carbides so that the matrix will resist or stop crack propagation through the added carbides, thus preventing catastrophic failure with substantially no decrease in achievable pressures, and consequent lengthening of service life.

This invention relates in general to ultra-high pressure devices for use in metal compaction.

More specifically, the invention relates to an improved anvil capable of sustaining the pressures encountered more efliciently and over substantially longer periods of anvil life than present state-of-the-art devices, and yet is several times more economical.

In particular, the present invention is applicable to ultra-high pressure devices achieving pressures of 40 kilobars and higher.

In such applications, extensive difiiculty has been encountered in presently available anvils due to the extremely short life resultant from the pressures achieved and particularly as a result of subtle misalignment and fracturing of the pressurized workpiece. As a result of this short life, harder and harder materials have been employed to endeavor to prevent breakage, often catastrophic, of the anvils. The harder the materials become, the more brittle the anvil system becomes and concurrently the more expensive it gets; mounting becomes more difi'icult, and maintenance tedious and expensive.

The most advanced anvils of the present art, arrived at after extensive and exhaustive research, employ diamonds on the pressure faces, as shown for example in National Bureau of Standards Journal of Physical Chemistry, vol. 63A, No. 1, 1959. Although satisfactory, such materials are obviously quite expensive and generally uneconomical.

The present invention obviates these and other difiiculties by departing from the ultra-hard materials concept and employing an anvil having carbide grains bonded by a high-speed steel alloy matrix which materially adds to the life of the anvil, is easy to manufacture, can be reworked, requires no special prestressing means, yet is readily available through commercial channels. Although the materials used in anvils of the present invention are known, and have been used in cutting tools, use was predicated on the known property of increased wear resistance and high heat resistance, both obviously requisite for high-speed metal cutting tools, but of no particular advantage in high pressure anvil work.

Other factors and many attendant advantages will become apparent when taken in conjunction with the following detailed description and drawings, in which:

FIGURE 1 is a plan view of a typical anvil;

FIGURE 2 is an elevational view of an anvil;

FIGURE 3 shows the anvils in their relationship to one another.

Referring now to FIGURES 1 and 2, a typical configuration of the anvils employed in ultra-high pressure devices is shown to comprise a cylindrical member ited States Patent 0 "ice having the upper portion thereof reduced by means of inclined surfaces 12 so that the pressure bearing face 14 is triangular in configuration and forms a work surface of known area substantially smaller than the area of base 16.

In application, as seen in FIGURE 3, the anvils 10 are so positioned in housings 20 (one of which is partially broken away) and that a volume 18 is formed between the faces 14 in which the workpiece or sample is compressed. The force applied by the motive means (not shown) is obviously concentrated at the face 14 and applied to a workpiece as pressure which results in compressive stresses through anvils 10.

It is the extremely high pressures exerted at these faces 14, which commonly achieve kilobars or about 1,450,000 pounds per square inch, that causes present anvils to break after only a few applications. This break can be catastrophic when under substantial loads, and may be dangerous because it permits the workpiece to be ununiformly confined, thereby permitting a shrapnel effect when the pressures equalize. This catastrophic failure is due to the total brittleness of the homogeneously ultra-hard materials to which the art has gone. The most common of these materials is tungsten carbide which has a very high hardness and modulus of elasticity, but is extremely brittle in the sense that it cracks rapidly and readily, is susceptible to notch sensitivity, and to unbalanced stresses and strains. It is, of course, necessary to reinforce or prestress these materials having ultra-high hardness with heat shrink fitted steel retaining jackets or rings.

The anvil of the present invention does not, like those of the present art, have a homogeneous extreme hardness. On the contrary, it comprises a steel bonded carbide wherein the steel matrix functions to stop or retard cracks between the carbide grains. When hardened, the highspeed steel matrix itself has a matrix of hard, highly alloyed martensite in which there are a very large quantity of hard particles of complex carbides of chromium, tungsten and vanadium. To this has been added additional material, such as titanium carbide, thus resulting in a material comprising hard carbide particles in a hardened high-speed steel matrix of martensite and complex carbides. One commercially available material consists of ultra-hard carbide grains in a high-speed steel alloy matrix.

Although the carbide grains may crack under extreme compressive or unbalanced stress, the crack usually will not instantly propagate across the matrix, thus materially lengthening the useful life of the anvil. In effect, the fracture point of the anvil composite is materially higher than known anvil systems. Although there is obviously some deformation in such an anvil due to the give of the matrix and theoretically a slightly less pressure on the workpiece may be exerted with the same input force, at 40 kilobars and above this difiterence is negligible and difficult to measure. The anvil of the present invention is also very readily heat treat-able and machinable in the annealed state on unsophisticated shop equipment and may thus be readily prepared and redressed. The anvils used in the present state-of-the-art are patently difficult to machine and cannot be heat treated.

Both titanium and tungsten carbide as well as crystallized boron nitride achieve the desired results when used with the matrix, the most important criteria being that the matrix or binder act as a crack propagation stop or limiter.

It will thus readily be apparent to those skilled in the art that an anvil for ultra-high pressure producing devices has been devised which overcomes the problems of the state-of-the-art, which is more economical to obtain, easier to maintain, and longer lived at the same pressures,

yet also possesses the pressure capabilities of the advanced present art anvils without the limitations imposed there on by brittleness.

I claim:

An anvil for the application of pressures of up to about 100 kilobars to a workpiece to be compacted comprising a heat treatable, high-speed tool steel bonded carbide material, said carbide being in the form of substantially individual ultra-hard grains encapsulated by a steel matrix, having a fracture resistance substantially higher than said carbide, said mixture being less brittle than said carbide and operative to substantially limit crack propagation to said encapsulated carbide grain so that unbalanced compressive stresses on said anvil exceed the fracture point of 4 only one material and thus are not critical and said anvil is usable Without prestressing support means.

Cemented Carbides by Schwarzbodf and Kieifer, Macmillan Co., 1960, Patent Office Library, TP77053,

10 pages 10 and 148.

WILLIAM J. STEPHENSON. Primary Examiner. 

